U.S. patent application number 13/168091 was filed with the patent office on 2012-12-27 for composite segment collimators for spect without dead zones.
Invention is credited to Eric G. Hawman, Gengsheng L. Zeng.
Application Number | 20120326059 13/168091 |
Document ID | / |
Family ID | 47360967 |
Filed Date | 2012-12-27 |
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United States Patent
Application |
20120326059 |
Kind Code |
A1 |
Hawman; Eric G. ; et
al. |
December 27, 2012 |
Composite Segment Collimators for SPECT Without Dead Zones
Abstract
A multi-view composite collimator includes a first parallel
collimator segment having a plurality of collimator channels
oriented at a first slant angle and a second parallel collimator
segment adjacent to the first parallel collimator segment having a
plurality of collimator channels oriented at a second slant angle
different from the first slant angle and a bridging collimating
element is provided between the first and second parallel
collimator segments, wherein radiation can pass through the
bridging collimating element.
Inventors: |
Hawman; Eric G.;
(Schaumburg, IL) ; Zeng; Gengsheng L.; (Salt Lake
City, UT) |
Family ID: |
47360967 |
Appl. No.: |
13/168091 |
Filed: |
June 24, 2011 |
Current U.S.
Class: |
250/505.1 |
Current CPC
Class: |
G21K 1/025 20130101 |
Class at
Publication: |
250/505.1 |
International
Class: |
G21K 1/02 20060101
G21K001/02 |
Claims
1. A multi-view composite collimator for a nuclear medicine imaging
system, the collimator comprising: a first parallel collimator
segment having a plurality of collimator channels oriented at a
first slant angle; a second parallel collimator segment adjacent to
the first parallel collimator segment and having a plurality of
collimator channels oriented at a second slant angle different from
the first slant angle; and a bridging collimating element provided
between the first and second parallel collimator segments, wherein
radiation can pass through the bridging collimating element.
2. The multi-view composite collimator of claim 1, wherein the
bridging collimating element is a slit-slat collimating
segment.
3. The multi-view composite collimator of claim 1, wherein the
bridging collimating element is a multi-channel collimating
segment.
4. The multi-view composite collimator of claim 2, wherein the
slit-slat collimating segment is configured to provide parallel
collimation in one direction and fan beam collimation in another
direction.
5. The multi-view composite collimator of claim 1, wherein the
multi-view composite collimator is a bilateral collimator and the
first and second parallel collimator segments are parallel slant
collimator segments.
6. The multi-view composite collimator of claim 1, wherein the
multi-view composite collimator is a multi-divergent beam or
multi-convergent beam composite parallel slant collimator.
7. A multi-convergent beam composite parallel slant collimator for
a nuclear medicine imaging system, the collimator comprising: a
plurality of parallel collimator segments, each parallel collimator
segment having a plurality of collimator channels oriented at a
slant angle that is different from the slant angle of an adjacent
parallel collimator segment; and at least one bridging collimating
element provided between any pair of parallel collimator segments,
wherein radiation can pass through the bridging collimating
element.
8. The multi-convergent beam composite parallel slant collimator of
claim 7, wherein the bridging collimating element is a slit-slat
collimating segment.
9. The multi-convergent beam composite parallel slant collimator of
claim 7, wherein the bridging collimating element is a
multi-channel collimating segment.
10. The multi-convergent beam composite parallel slant collimator
of claim 8, wherein the slit-slat collimating segment is configured
to provide parallel collimation in one direction and fan beam
collimation in another direction.
Description
FIELD OF THE DISCLOSURE
[0001] The disclosure is related in general to systems and methods
used in radiation imaging, and more particularly to systems and
methods for eliminating dead spots in composite segment collimators
used in SPECT imaging.
BACKGROUND
[0002] In conventional radiation imaging arrangements, collimators
are used to permit only beams of radiation emanating along a
particular path to pass a selected point or plane. Collimators are
frequently used in radiation imagers to ensure that only radiation
beams passing along a direct path from the known radiation source
strike the detector thereby minimizing detection of beams of
scattered or secondary radiation.
[0003] Particularly in radiation imagers used for medical
diagnostic analysis or for non-destructive evaluation procedures,
it is important that only radiation emanating from a known source
and passing along a direct path from that source be detected and
processed by the imaging equipment. If the detector is struck by
undesired radiation such as that passing along non-direct paths to
the detector, performance of the imaging system can be
compromised.
[0004] One diagnostic technology that incorporates collimators is
the gamma camera typically utilized in Single Photon Emission
Computed Tomography (SPECT) scanning, which is a nuclear medicine
procedure in which gamma camera(s) have traditionally rotated
around the patient taking pictures from multiple angles. From these
images, a computer is employed to form a tomographic image of the
internal area-of-interest within the patient using a calculation
process that is similar to that used in X-ray Computed Tomography
(CT) and in Positron Emission computed Tomography (PET).
[0005] In the instance of SPECT scanning, a subject (patient) is
infused with a radioactive substance that emits gamma rays.
Conventionally, a gamma camera includes a transducer to receive the
gamma rays and record an image therefrom. In order for the image to
be a true representation of the subject being investigated, a
collimator having collimating apertures is positioned between the
transducer and the subject to screen out all of the gamma rays
except those directed along a straight line through the collimating
apertures between a particular part of the subject and a
corresponding particular part of the transducer. Traditionally, the
collimator is made of a radiopaque material such as lead and has
collimating apertures, which have been formed therein by various
means such as drilling, casting, or lamination of corrugated strips
of lead foil.
[0006] With current systems, the number of angular views that can
be acquired of a target organ, (e.g. the heart), by a SPECT gamma
camera is restricted to one-view per gantry stop per detector.
Acquisition of multiple views requires rotation (or at least
movement) of the camera. Hence, tomographic imaging of rapid tracer
dynamics (uptake and washout from various tissue and metabolic
compartments) is difficult due to the necessity of scanning large
massive detectors rapidly.
[0007] Bisegmental collimators, such as those described in U.S.
Pat. No. 4,659,935 to Hawman, are known for improving the
sensitivity of SPECT in imaging small organs. Recently,
multisegmental diverging collimation has been proposed as method
that can achieve higher sensitivity than multipinhole SPECT
systems. It has also been realized that multisegment parallel
collimation, using parallel-hole segments, but having different
slant angles, can provide even more sensitivity for the same system
spatial resolution.
[0008] Fabrication of a multi-view composite collimator entails the
abutment of multiple collimator segments having large differences
in the direction of view. Since multichannel collimators are
typically formed from lead, which has a finite attenuation
coefficient for gamma rays, the collimator is of finite thickness,
typically a few (e.g., 2 to 4) centimeters. Regions between
collimator segments in such composite collimators are often filled
with a radiopaque material, such as lead. This results in gaps
(i.e., uncollimated space) on the detector, which have a width
approximately equal to the collimator thickness times the sum of
the tangents for the slant angle of the abutting slanted collimator
segments.
[0009] It would be desirable to minimize such gaps or dead zones in
multi-view composite collimators in order to maximize the amount of
collimated area of the detector. Such an arrangement should improve
the sensitivity and imaging speed of a SPECT systems.
SUMMARY
[0010] An improved multi-view composite collimator for nuclear
medicine imaging systems according to the present disclosure in
which the dead spaces between two adjoining collimator segments are
eliminated is disclosed. In one embodiment of the present
disclosure, the dead space on the detector is eliminated by filling
the dead zone with a bridging collimating element. In one
embodiment, the bridging collimating element is a slit-slat
collimation segment. In another embodiment, the bridging
collimating element is a multi-channel collimator segment.
[0011] The multi-view composite collimator comprises a first
parallel collimator segment having a plurality of collimator
channels oriented at a first slant angle and a second parallel
collimator segment adjacent to the first parallel collimator
segment. The second parallel collimator segment has a plurality of
collimator channels oriented at a second slant angle different from
the first slant angle. The multi-view composite collimator further
comprises a bridging collimating element provided between the first
and second parallel collimator segments, wherein radiation can pass
through the bridging collimating element.
[0012] According to another aspect of the present disclosure, the
multi-view composite collimator can be a multi-divergent beam
composite parallel slant collimator that comprises a plurality of
parallel collimator segments and at least one bridging collimating
element provided between two adjoining parallel collimator
segments.
[0013] The use of the disclosed multi-view collimator will enable
utilization of areas of the detector that conventionally were
unused dead spaces at the interface regions between two adjoining
composite collimator segments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The accompanying drawings illustrate preferred embodiments
of the disclosure so far devised for the practical application of
the principles thereof, and in which:
[0015] FIG. 1 is a cross-sectional view of a first embodiment of a
system used in imaging the patient tissue region;
[0016] FIG. 2 shows a front view of the collimator 18 of FIG.
1;
[0017] FIG. 3 is a schematic illustration of images formed by the
collimator 18 on the camera's crystal detector surface;
[0018] FIG. 4 is a side view of two adjoining parallel slant
collimator segments.
[0019] FIG. 5 shows a perspective view of a slit-slat collimator
segment embodiment of a bridging collimating element according to
an embodiment of the present disclosure.
[0020] FIG. 6 shows a perspective view of the slit-slat collimator
segment bridging collimating element filling the formerly dead
space between two adjoining slant collimator segments.
[0021] FIG. 7 shows a side view of a multi-channel collimator
embodiment of a bridging collimating element according to an
embodiment of the present disclosure.
[0022] FIG. 8 shows a perspective view of a seven-segment
multi-divergent beam composite parallel slant collimator.
[0023] FIG. 9 shows a patient-side view of a seven-segment
multi-divergent beam composite parallel slant collimator.
[0024] FIG. 10 shows a perspective view of the seven-segment
multi-divergent beam composite parallel slant collimator of FIG.
9.
DETAILED DESCRIPTION
[0025] FIGS. 1-3 show an example of a multi-view composite
collimator 18, which in this particular example is a bilateral
collimator. FIG. 2 shows a front view of the collimator 18. The
bilateral collimator 18 is divided into two groups or segments 24,
26 of collimating holes or passageways 28. The passageways 28
within each segments 24, 26 are oriented parallel to each other but
the two groups of passageways are oriented in different directions,
in other words in different viewing angles, as shown in FIG. 1. In
essence, each of the segments 24 and 26 of the bilateral collimator
18 is a slanted parallel collimator. The result is that the two
segments 24, 26 of the collimator simultaneously produce two views
20 and 22 of the a targeted tissue region 2 of a patient 10, such
as a heart, on the detector surface 16 of the gamma camera 4. The
views 20 and 22 of the tissue region 2 are defined by the
directions of the first segment 24 and the second segment 26 of
passageways 28 in the multi-view bilateral collimator 18. The
multi-view collimator 18 is made of a radiation-absorbing material,
which in one embodiment is lead. Thus, obliquely directed radiation
is absorbed by the collimator 18 and only radiation which is
parallel to the passageways 28 will reach the detector surface
16.
[0026] In this embodiment, the orientation of the passageways 28 in
the first and second slanted parallel collimator segments 24 and 26
are mirror images of each other, so their constituent passageways
28 are symmetrical (i.e. they make equal angles a with a line
normal to the detector surface 16 when the collimator 18 is mounted
to the camera 4). None of the passageways 28 in the first segment
24 intersects any of the passageways 28 in the second segment 26.
Thus, the first and second views 20 and 22 do not overlap.
[0027] Because the collimator passageways 28 in each segment are
slanted towards the intended target tissue region being imaged,
there is a gap or a dead space 46 at the interface region between
the two segments 24, 26 on the detector side of the collimator 18.
This can be better seen in the side cross-sectional view of the
bilateral collimator 18 shown in FIG. 4. In FIG. 4, the detector
surface 16 is on the bottom side of the illustration and the
patient side is on the top side. The dead space 46 exists between
the two segments 24 and 26 as shown. The dead space 46 is a gap
that is wider on the detector side of the collimator 18 than the
patient side. The dead space 46 has a width W on the detector side
and a narrower width 52 on the patient side and a cross-section of
the dead space 46 forms a trapezoid. In conventional multi-view
composite collimators, the dead spaces 46 are filled with lead. The
lead filler absorbs incoming gamma rays, which if they could be
captured by the detector would increase the sensitivity of the
SPECT imaging system.
[0028] According to an embodiment of the present disclosure, an
appropriately shaped bridging collimating element is provided in
the interface region filling the dead space 46 in order to make the
dead space useful. In this example, the bridging collimating
element is a slit-slat collimator segment 48 shown in FIG. 5. The
slit-slat collimator segment 48 comprises a plurality of
trapezoidal-shaped slat elements 50 spaced apart by a distance G,
thus forming slits between the slat elements 50. Each of the slat
elements 50 has a thickness of WT. Each of the slat elements 50 has
a trapezoidal shape that matches the cross-section of the dead
space 46. The slat elements have a width W at the wide end (the
detector side) and a width 52 at the narrow end (the patient side)
as shown. The actual dimensions G, WT, W and 52 is to be
appropriately determined according to the particular collimator
dimensions and application. For example, referring to the
configuration shown in FIG. 4, the detector side width W of the
slat elements 50 can be determined according to the formula
W=t*(tan .theta..sub.1+tan .theta..sub.2), where t is the thickness
of the collimator 18 and .theta..sub.1 and .theta..sub.2 are the
slant angles of the passageways 28 in the two adjacent collimator
segments 26 and 24, respectively.
[0029] FIG. 6 shows a perspective view of the bilateral collimator
18 where the slit-slat collimator segment 48 is provided in the
interface region between the two adjoining collimator segments 24
and 28. By filling the conventionally dead space 46 in the
interface region of the collimator 18 with the slit-slat collimator
segment 48, that portion of the collimator 18 does not completely
absorb the gamma rays and thus the sensitivity of the SPECT gamma
camera 4 is increased.
[0030] According to another embodiment of the present disclosure,
the bridging collimating element can be a multichannel collimator
segment 68 shown in FIG. 7.
[0031] Similar to the bilateral collimator 18 discussed above,
another example of multi-view composite collimators,
multi-convergent beam composite parallel slant collimators also
have dead spaces between each of the several collimator segments.
According to another aspect of the present disclosure, the dead
spaces in multi-convergent beam composite parallel slant
collimators can be made useful by providing a bridging collimating
element (a slit-slat collimating segment 48 or a multi-channel
collimating segment 68) in the interface region between each pair
of adjacent collimating segments.
[0032] FIGS. 8-10 show various views of a multi-convergent beam
composite parallel slant collimator 180. The multi-convergent beam
composite collimator is comprised of several collimator segments a,
b, c, d, e, f, and g. Each of the collimator segments a-g has a
different viewing angle and each forms an image of the target
tissue region 2 on the detector surface 16.
[0033] FIGS. 9 and 10 show a plan view and a perspective view,
respectively, of the multi-divergent beam composite parallel slant
collimator 180 from the patient side. Each of the collimator
segments a-g is a parallel beam collimator (i.e., the passageways
in each segment are in parallel arrangement) but each segment has
different viewing angle. Generally, the center segment d is an
orthogonal parallel beam collimator. Because of the different
viewing angles of each segment a-g, dead spaces exist at the
interfaces 185 between any two adjacent collimator segments a-g,
similar to the bilateral collimator 18. According to an embodiment
of the present disclosure, these dead spaces are filled with
bridging collimating elements (48 or 68) as illustrated in FIG. 10.
In FIG. 10, three of such bridging collimating elements 48b-e,
48e-g, and 48f-g can be seen. The bridging collimating element
48b-e is a slit-slat collimating segment filling the gap between
the collimator segments b and e. The bridging collimating element
48e-g is a slit-slat collimating segment filling the gap between
the collimator segments b and g. The bridging collimating element
48f-g is a slit-slat collimating segment filling the gap between
the collimator segments f and g.
[0034] For each of the embodiments discussed herein, the bridging
collimating elements 48, 60 provide an additional image, albeit one
that is strongly anamorphic, of the target tissue region 2 to
thereby improve sensitivity of the overall system. By anamorphic it
is meant that the scale or magnification of the image differs in
the orthogonal directions, one direction being parallel to the gap
between the two adjacent collimator segments, and the other
direction transverse to the gap.
[0035] According to another embodiment of the present disclosure,
multi-divergent beam composite parallel slant collimators are
another example of multi-view composite collimators in which the
bridging collimating element of the present invention can be
applied to eliminate dead spaces.
[0036] The disclosed system improves the speed of the multiview
collimator for stationary SPECT acquisition. For improved angular
sampling, it can also be used in a rotating gamma SPECT system that
uses a multiview collimator. The disclosed system and method can
also be used for a collimator in a multi-head detector SPECT
cardiac system with sensitivity about 4 to 5 times of a
dual-detector parallel beam collimator camera. The system would
provide sufficient views for stationary acquisition of cardiac
images. This would simplify imaging for studies having fast tracer
kinetics. It could also be used to advantage for gated cardiac
SPECT studies.
[0037] Alternatively, disclosed system can be used in a
multihead-detector SPECT system where the number of angular views
that the system steps through during acquisition is reduced due to
the increase in the number of views obtained using a multiview
collimator for each angular step of the gantry.
[0038] Although this invention has been described with reference to
particular exemplary embodiments, it is to be understood that the
embodiments and variations shown and described herein are for
illustration purposes only. Modifications to the current design may
be implemented by those skilled in the art, without departing from
the scope of the invention.
* * * * *